Dipole interaction of particles in magnetic fluid stabilized by a double layer of surfactant in water

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Purpose of the work: to study the influence of interparticle dipole-dipole interactions on the susceptibility of a magnetic fluid stabilized by a double layer of surfactant in water.Research method consists in measuring the initial differential susceptibility of a magnetic fluid depending on its concentration. Three samples of fluid based on magnetite particles, differing in the composition of the stabilizing shells, were studied. The following acids were used as the first layer of the stabilizer: lauric (C12), decanoic (C10) and octanoic (C8). The second layer of the stabilizing shell was formed by sodium dodecyl sulfate with a small proportion of the corresponding acid. Susceptibility measurements were performed on a setup for measuring magnetization curves. The concentration of the samples was determined by their saturation magnetization.Results. The concentration dependences of the initial susceptibility were measured for three samples of magnetic fluid based on magnetite particles. The obtained results were compared with theoretical models of the modified effective field of A.O. Ivanov and the average-spherical one. Both theories predict overestimated values of susceptibility in relation to experimental values. The modified effective field theory overestimates the results by 20%. The mean-spherical model - by 12%. It is shown that the correct interpretation of the concentration dependence of the susceptibility of magnetic fluid samples is possible only by approximating the ratio of susceptibility to saturation magnetization. Based on this approximation, an empirical formula in the form of a third-degree polynomial with a negative cubic term is proposed to describe the concentration dependence of susceptibility.Conclusion. Thus, the obtained results require the construction of new or modification of old theories of dipole-dipole interaction of magnetic particles in aqueous colloidal solutions with stabilization of particles by a double layer of surfactant.